1. Field of the Invention
The present invention relates to dielectric filters, duplexers, and communication devices incorporating the same, which are used in base stations having high-frequency communication apparatus.
2. Description of the Related Art
A conventional dielectric filter 110 will be illustrated with reference to FIGS. 11 and 12. FIG. 11 is a side view of the conventional dielectric filter 110, and FIG. 12 is a plan view thereof. In these figures, shield cases are cut away to show the inside of the filter 110.
As shown in FIGS. 11 and 12, the conventional dielectric filter 110 comprises a cylindrical dielectric resonator 111, a supporting base 112 for supporting the dielectric resonator 111, and a metal shield case 113 for containing the dielectric resonator 111 and the supporting base 112. In addition, a loop 115 as an input coupling unit and a probe 116 as an output coupling unit are attached to the shield case 113 such that the loop 115 and the probe 116, respectively, are coupled to the dielectric resonator 111.
In this arrangement, the loop 115 is formed by connecting an end of a metal line or a metal plate to the shield case 113 to be grounded, and connecting the other end thereof, for example, to the central conductor of a coaxial connector so as to perform a magnetic-field coupling with the dielectric resonator 111. In general, a loop has a structure in which one end of the loop is connected to a shield case, and the other end thereof is connected to a central conductor to retain both ends of the loop. This structure permits filter characteristics to be stabilized, since the position of the loop does not change due to influence from the outside, and the amount of coupling can be maintained constant.
Meanwhile, regarding the probe, an electric-field coupling is performed between the probe and a dielectric resonator by making an end of a metal line open, and connecting the other end thereof, for example, to the central conductor of a coaxial connector. In the electric-field coupling between the probe and the dielectric resonator, the amount of coupling with the dielectric resonator is larger than the amount of coupling between a dielectric resonator and a loop having the same length as that of the probe.
In the conventional dielectric filter 110 having such a structure, a signal is inputted from the loop 115 as the input coupling unit so as to couple the loop 115 with the TE 01xcex4 mode of the dielectric resonator 111. After this, the dielectric resonator 111 and the probe 116 as the output coupling unit are coupled so as to output only the signals of a specified frequency band.
As an input coupling unit and an output coupling unit, besides the combination of a loop and a probe, the combination of only loops, and the combination of only probes are conventionally known.
Next, referring to FIGS. 13 and 14, a description will be given of a multi-mode dielectric filter proposed by the assignee of the present application in Japanese Patent Application No. 10-220371 which was not laid-open to the public at the time of the priority date of this application. Thus, the disclosures of the drawings as well as the contents of the Japanese application do not constitute prior art. FIG. 13 is a side view of the multi-mode dielectric filter denoted by reference numeral 120, and FIG. 14 is a plan view thereof. In each of these figures, a shield case is cut away to show the inside of the filter.
As shown in FIGS. 13 and 14, the multi-mode dielectric filter 120 comprises a dielectric resonator 121, a supporting base 112 for supporting the dielectric resonator 121, and a metal shield case 113 containing the dielectric resonator 121 and the supporting base 112. In addition, a loop 125a as an input coupling unit and another loop 125b as an output coupling unit are attached to the shield case 113 so that the loops 125a and 125b are respectively coupled with the dielectric resonator 121.
The dielectric resonator 121 has a configuration seen as if it were formed by cutting away four corners of a square when observed from above. With this configuration, the dielectric resonator 121 can be used as a triple-mode dielectric resonator, which resonates in three resonant modes shown in FIG. 5, such as the TM 01xcex4x+y mode, the TE 01xcex4Z mode, and the TM 01xcex4xxe2x88x92y mode. In this case, each of the subscripts x, y, and z indicates each of the directions of x, y, and z set as an axial direction. For example, the TM 01xcex4x+y mode is equivalent to the TM 01xcex4 mode obtained when the sum of a vector x and a vector y is set as the axial direction. The axis z indicates upper and lower directions, and the electric field is indicated by a solid line, whereas the magnetic field is indicated by a broken line.
In the multi-mode dielectric resonator 120 having such a structure, the loop 125a as the input coupling unit is positioned in a direction perpendicular to the magnetic field of the TM 01xcex4x+y mode so as to couple the loop 125a and the TM 01xcex4x+y mode of the dielectric resonator 121. Then, the TM 01xcex4x+y mode and the TE 01xcex4Z mode are coupled, and furthermore, the TE 01xcex4Z mode and the TM 01xcex4xxe2x88x92y mode are coupled. Lastly, the TM 01xcex4xxe2x88x92y mode of the dielectric resonator 121 is coupled with the loop 125b as the output coupling unit positioned in a direction perpendicular to the magnetic field of the TM 01xcex4xxe2x88x92y mode. This structure permits the multi-mode dielectric filter 120 to serve as a three-stage band pass filter.
In the conventional dielectric filter, both the input coupling unit and the output coupling unit are positioned on the upper side of the dielectric resonator. In this case, the positions of the input coupling unit and the output coupling unit are determined by considering the amount of coupling between the input coupling unit and the dielectric resonator, and the amount of coupling between the output coupling unit and the dielectric resonator.
However, as shown above, when the input coupling unit and the output coupling unit are relatively close to each other, a relatively great mutual influence is generated between the input coupling unit and the output coupling unit. Therefore, when the positions for arranging both the input coupling unit and the output coupling unit are determined, it is necessary to consider the mutual influence generated between the coupling units. This makes designing of the filter difficult. Similarly, this problem often occurs in a case in which an input coupling unit and an output coupling unit are disposed on the side positions of the dielectric resonator.
In contrast, in the multi-mode dielectric filter proposed in Japanese Patent Application No. 10-220371, the two resonant modes orthogonal to each other are coupled to the input coupling unit and the output coupling unit. As a result, in order not to make the input coupling unit and the output coupling unit mutually intersect in a space-limited structure, it is necessary to reduce the lengths of both the input coupling unit and the output coupling unit.
Meanwhile, in order to increase the amount of coupling between the dielectric resonator and the input coupling unit, and the amount of coupling between the dielectric resonator and the output coupling unit, it is necessary to increase the lengths of the input coupling unit and the output coupling unit. However, in such a dielectric filter, due to a space limitation in the structure, the lengths of the input coupling unit and the output coupling unit must be reduced. Furthermore, the loops are used as the input coupling unit and the output coupling unit. Thus, no great amount of coupling can be obtained. In other words, in the multi-mode dielectric filter proposed in Japanese Patent Application No. 10-220371, in addition to the above problem, when filter characteristics with a broad pass bandwidth are required, it is impossible to increase the amounts of coupling between the dielectric resonator and the respective coupling units. As a result, there is a problem in that the desired filter characteristics can not be obtained.
Accordingly, it is an object of the present invention to solve the above problems and provide a dielectric filter, a duplexer, and a communication apparatus incorporating the same, in which the positions of an input coupling unit and an output coupling unit can be easily arranged, and the amounts of couplings between a dielectric resonator and the coupling units can be sufficiently obtained.
To this end, according to a first aspect of the present invention, there is provided a dielectric filter including a shield case having conductivity; a dielectric resonator disposed inside the shield case; a supporting base integrally formed with the dielectric resonator or separately formed therefrom so as to support the dielectric resonator; an input coupling unit and an output coupling unit for coupling to the dielectric resonator; in which one of the input coupling unit and the output coupling unit is a probe with an open-circuited end, the probe extending on a side where the supporting base of the dielectric resonator is disposed.
When one of the input coupling unit and the output coupling unit extends on the side where the supporting base of the dielectric resonator is disposed, the input coupling unit and the output coupling unit are positioned such that the units do not influence each other. As a result, designing for positioning the input coupling unit and the output coupling unit can be easily performed. Furthermore, since the coupling unit extending on the side where the supporting base is disposed is formed by the probe, it is not necessary to increase the length of the coupling unit in order to obtain a desired amount of coupling, and there is no problem in that the limitation to the length of the coupling unit caused by the presence of the supporting base hinders obtaining a sufficient amount of coupling.
In addition, in the above dielectric filter, the dielectric resonator may be a multi-mode dielectric resonator having at least two resonant modes substantially orthogonal to each other.
When the input coupling unit and the output coupling unit are disposed so as to be coupled to the multi-mode dielectric resonator having at least two resonant modes substantially perpendicular to each other, directions in which the input coupling unit and the output coupling unit extend are equivalent to directions toward the center of the dielectric resonator when observed from above. With the structure of this dielectric filter, it is easy to design the positions for arranging the input coupling unit and the output coupling unit and obtain a sufficient amount of coupling. That is, in this dielectric filter, since the input coupling unit and the output coupling unit are disposed away from each other so as to prevent influence on each other, and the coupling unit extending on the side where the supporting base is disposed is formed by the probe, it is not necessary to increase the length of the coupling unit in order to obtain the desired amount of coupling, and the presence of the supporting base does not hinder the extending unit from coupling with the resonator.
In addition, according to a second aspect of the present invention, there is provided a duplexer including at least two filters; input/output connecting units connected to the filters; and an antenna connecting unit commonly connected to the filters; in which at least one of the filters is the dielectric filter in accordance with the first aspect of the invention.
In addition, according to a third aspect of the present invention, there is provided a communication apparatus including the duplexer in accordance with the second aspect of the invention; a transmission circuit connected to at least one of the input/output connecting units of the duplexer; a reception circuit connected to at least one of the input/output connecting units, which is not the input/output connecting unit connected to the transmission circuit; and an antenna connected to the antenna connecting unit of the duplexer.
This arrangement can provide a duplexer and a communication apparatus, in which designing for positioning the input coupling unit and the output coupling unit can be facilitated, and required characteristics can be obtained.